How to exercise in a heat wave

Julie Deardorff, Tribune Newspapers

Heat does more than make us crabby and lethargic; it can be deadly, and not just for the elderly. The minute we’re blasted by suffocating heat, our bodies tenaciously fight to defend our core temperature of 98.6 degrees Fahrenheit, as I detailed in “How extreme heat affects the body.” But they don’t always succeed, especially in humid weather that prevents sweat from evaporating.

If you’re unfit, overweight or suffering from a medical condition such as diabetes or cardiovascular disease, your body will have a harder time adapting to this week’s extreme heat, so consider exercising in an air-conditioned facility.

But if you’re ready to sweat it out in the blistering outdoors, here are some ways to do it safely:

Choose water. If you’re going to exercise for less than an hour, water is generally the best hydration fluid, Bryan said. If you’re out for longer than 60 minutes, a sports drink may be the more beneficial.

Adequately hydrate: Hydration is important but you don’t have to obsess over it. Drinking too much water leads to hyponatremia, an imbalance of water to salt in the body. “Drink copious amounts of fluid (just short of feeling fully bloated) thirty minutes before exercise, drinking at least six ounces of fluid after approximately every 20 minutes of exercise, and drinking beyond thirst cessation during the recovery period,” said Cedric Bryant, chief science officer of The American Council on Exercise. Still, other experts say general drinking guidelines for the masses are a bad idea because not everyone needs the same amount of fluid, men and women have different sweat rates and your needs change as you acclimate. The best thing is to listen to your body; it will tell you if you've been drinking enough water.

Check your urine color: If your urine is the color of lemonade, you’re adequately hydrated. If it’s the color of apple juice or iced tea, have a glass of water, said Matthew Ganio, a researcher at the Institute for Exercise and Environmental Medicine at UT Southwestern Medical Center and Texas Health Presbyterian Hospital. “Even in the heat, if you’re exercising less than an hour and you go into it well hydrated and have some food afterward, you’ll be fine,” he said.

Go slow. Exercise intensity drives internal temperature more so than anything else. Slowing down the pace will do more for you than drinking an extra glass of water. Also exercise early in the morning before it gets even hotter and wear minimal clothing, said Ganio.

Ditch the rubberized sweat suit. Or even the soggy wet cotton t-shirt. Clothing that is impermeable to water prevents the evaporation of sweat from the skin. If your sweat can’t evaporate, your body can’t cool down. This is also why dumping a glass of water on your head isn’t very effective.

Acclimatize: If you have several weeks, go out for short periods and move more slowly than normally. Eventually, you’ll sweat sooner, produce more sweat, and lose fewer electrolytes, said Bryant. This will lower your body core temperature, decrease the heart rate’s response to exercise, and reduce the chances of dehydration.

Use the 90/60 rule: Consider curtailing exercise when the ambient temperature is above 90 degrees Fahrenheit and the relative humidity is above 60 percent, said Bryant..